Atmosphere

Air toxics and indoor air quality in Australia

State of knowledge report
Environment Australia, 2001
ISBN 0 6425 4739 4

Part C: Factsheets (continued)

Fluoride compounds

Substance name: Fluoride compounds
CASR number: Not applicable
Molecular formula: Fluoride: F-
Hydrofluoric acid: HF
Sodium fluoride: NaF
Synonyms: Fluoride: CASR # 16984-48-8
Hydrogen fluoride (hydrofluoric acid): CASR # 7664-39-3
Sodium fluoride: CASR # 7681-49-4

Physical and chemical properties

Melting point: Hydrogen flouride: -83.55°C, Sodium flouride: 993°C
Boiling point: Hydrogen flouride: 19.5°C, Sodium flouride: 1700°C
Vapour density: Hydrogen flouride: varies with temperature; Sodium flouride: not applicable (solid)
Specific gravity: Hydrogen flouride: 0.993, Sodium flouride: 2.558

Fluoride compounds contain one or more atoms of the element fluorine. Fluorine (F2) itself is a yellow-green gas with a strong, sharp odour (like pool chlorine) but the main source of the element is the mineral fluorspar (CaF2). An important inorganic fluorine-based chemical is hydrogen fluoride, a colourless gas with a strong, irritating odour, which also exists as a liquid at temperatures below 19.5°C. Hydrogen fluoride dissolves in water to make hydrofluoric acid of various strengths. Hydrogen fluoride and hydrofluoric acid will corrode many substances, including glass and most metals. Hydrogen fluoride is used to manufacture other fluorine-based chemicals, including sodium fluoride, which is a white powder (sometimes dyed blue for identification purposes). Hydrofluoric acid can also be formed by acidifying other fluoride compounds.

Common uses

Hydrogen fluoride is the industrial starting point for organic and inorganic fluorine-based chemicals, including chlorofluorocarbons (CFCs) and their substitutes, and polymers such as teflon, aluminum fluoride, sodium fluoride and other fluoride salts; it is also used to separate uranium isotopes. In Australia, hydrogen fluoride (anhydrous) is mainly used as a catalyst in petroleum refining. Hydrofluoric acid is also used widely in Australia in different strengths. Most use is in metal treatment and cleaning; laboratory analysis, etching of glass, ceramics, brick and stone; and rust removal. Specific uses include removing graffiti, antislip floor treatment, repairing printing plates, cleaning mag wheels, spot removal in laundries, carpet and drycleaning, and oil drilling; it is also used in dental laboratories and in the manufacture of semiconductors and solar cells.

Sources of emissions

Diffuse and point sources

Fluoride emissions can occur from the industries that either manufacture or use fluorine-based chemicals. In addition, hydrogen fluoride is produced incidentally during the manufacture of aluminium, phosphate fertilisers, ceramics, bricks and clay and in the combustion of coal. Particulate fluorides may also be released. Toothpaste and fluoridated water are other sources.

These emissions may be to the soil, water, or air.

Natural sources

Fluorine is a naturally occurring element in the earth, but elemental fluorine is too reactive to be found alone in nature; rather, it is found as part of the mineral fluorspar. Water in rivers or streams that flow over rocks rich in fluorine-containing minerals such as fluorspar may naturally contain dissolved fluoride. Hydrogen fluoride may enter the environment from natural sources such as volcanoes, weathering of minerals and marine aerosols.

Mobile sources

There are no known mobile sources.

Consumer products which may contain fluoride compounds

Products include toothpaste, pesticides, ceramic and glass polishing etching and frosting materials, special dyes, some metal cleaners (mag wheel) and rust removers. In some areas, drinking water is naturally or artificially enriched in fluoride.

Health effects

How might I be exposed to fluoride compounds?

Workers in the industries that use or produce fluoride compounds are at greatest risk of exposure. Consumers are most likely to be exposed to fluoride compounds when using consumer products containing fluoride compounds, especially toothpaste or fluoride-enhanced water. Accidental exposure to rust removers or cleaners could also occur. Residents in close proximity to production and processing facilities using fluoride compounds may also receive very low levels of fluoride exposure.

By what pathways might fluoride compounds enter my body?

Fluoride compounds may enter the body by inhalation, ingestion or skin contact.

Health guidelines

National Occupational Health and Safety Commission (NOHSC):

Fluorine is listed as a substance under review for irritant effects by the NOHSC.

Australian Drinking Water Guidelines (NHMRC and ARMCANZ 1996):

What effect might fluoride compounds have on my health?

Fluorides are everywhere throughout the environment, but at very low levels that are not believed to be harmful. Small amounts of sodium fluoride help prevent tooth decay, but high levels may harm your health. In children whose teeth are forming, excessive fluoride levels may cause dental fluorosis with visible changes in the teeth. In adults, high fluoride over a long time may lead to skeletal fluorosis with denser bones, joint pain, and limited joint movement. This is rare. High levels of fluorine or hydrogen fluoride gas are toxic and corrosive and can cause death, as can concentrated hydrofluoric acid. At low levels these substances can irritate the eyes, skin and lungs. Contact with hydrofluoric acid (even diluted) or solutions of acidified fluoride compounds can burn the eyes (causing blindness) and skin, causing severe burns deep beneath the skin and damaging internal tissues. This can occur hours after contact, even if no pain is initially felt. Contact with hydrofluoric acid happens mainly in the workplace.

Environmental effects

Environmental fate

Hydrogen fluoride may enter the air during production, use and transportation. The gas dissolves in clouds, fog, rain or snow. This enters the environment as wet acid deposition ('acid rain'). In the environment it will react with other chemicals (ammonia, magnesium, calcium) to form salts, neutralising the acid.

Environmental transport

Industrial emissions of fluoride compounds can produce elevated concentrations in the atmosphere. Hydrogen fluoride can exist as an aerosol or mist, which may dissolve in clouds, fog, rain, dew, or snow. In clouds and moist air it will travel along the air currents until it is deposited as wet acid deposition (acid rain, acid fog, etc). In waterways it readily mixes with the water.

Environmental guidelines

There are no national guidelines.

What effect might fluoride compounds have on the environment?

Hydrogen fluoride can exist as an aerosol or mist in the air if released to the atmosphere. It dissolves when mixed with water. Insufficient data are available to predict the short-term or long-term effects of hydrogen fluoride on aquatic life, plants, birds or land animals. Concentrated hydrogen fluoride is very corrosive and would badly burn any plants, birds or land animals exposed to it. The concentrations of hydrogen fluoride found in close proximity to sources may adversely affect some species of plants. Small quantities of hydrogen fluoride will be neutralised by the natural alkalinity of aquatic systems. Larger quantities may lower the pH for extended periods of time. Fluorides are not expected to bioaccumulate.

Key

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